Non-linear amplifiers such as logarithmic amplifiers find wide application especially in the communication field and in measurement instruments, such as, spectrum analyzers, sampling oscilloscopes, and time domain reflectometers for measuring the characteristics of electrical or optical signal transmission lines.
The input signal to be processed in the amplifier system of a measurement instrument such as a fiber optic time domain reflectometer may have a dynamic range which exceeds the dynamic range of a conventional linear amplifier. In order to permit use of such conventional linear amplifiers, the input signal is first processed by a circuit having a non-linear (e.g. logarithmic) transfer function, so as to compress the dynamic range of the input signal and thereby increase the apparent dynamic range of the overall amplifier system.
The dynamic range of the amplifier system may be increased further by using a linear preamplifier to amplify very weak signal components. A conventional preamplifier, however, cannot accept stronger signal levels, and thereby limits the dynamic range of the amplifier system in which it is used.